Add documentation of catalogues

The project members have prepared good documentation about the contents and peculiarities of all our catalogues. This information will be important for the users of the VRE (as discussed on 2023-08-08). Where should we put this documentation, and how do we pass this on to the VRE?

The issue names no files, tests, or entry points. Start by reviewing the prepared catalogue documentation and how the VRE currently receives project information. Done means deciding where the catalogue documentation belongs and establishing how it will be passed to VRE users.

Written by the indexing model from the issue text.